Chromium-titanium steel adapted for sealing to glass



Patented Mar. 16, 1954 CHROMIUM-TITANIUM STEEL ADAPTED FOR SEALING T GLASS Freeman J. Phillips and Raymond Smith, Pittsburgh, Pa., assignors to United States Steel Corporation, a corporation of New Jersey N 0 Drawing.

3 Claims. 1

This invention relates to a steel of novel composition having a coefficient of thermal expansion which renders it particularly valuable for making metal-to-glass seals. Certain modern metal-to-glass seals present a problem of considerable difliculty. One of these is the kinescope or television screen tube which usually comprises a, metal cone, a glass disc overlying the large end thereof and a glass tube afiixed coaxially to the small end. The metal of which the cone is composed must have a thermal co efiicient of expansion such that a wide variation in temperature, i. e., from the temperature at which the seal is formed, about 1200 C., to room temperature, will not fracture the glass as a result of differential contraction. After completion of the seal, furthermore, the glass portion thereof must not show substantial residual strain since such strain, if excessive, increases the danger of breakage by the shock or impact incident to handling and shipping. The metal, moreover, must have sufficient ductility to permit spinning the cone-shaped body of the tube from a piece of fiat sheet. While certain known alloys have substantially the same coefficient of thermal expansion as the glass used to form the disc and small end of the tube, e. g., about 10.2)(- inches per degree 0., they cannot be spun into tube bodies. Conversely, conventional steels having the requisite spinning quality cannot be employed because they oxidize too readily and have thermal coeflicients differing too widely from that of the glass.

We have discovered a novel ferrous alloy which satisfactorily meets all the requirements of the trade in respect to scaling with glass, i. e., gastightness, ductility and an expansion coefficient giving a residual strain not over 200 millimicrons per cm. as determined by examining with a polariscope a bead of glass fused to a sheet of the alloy. Our improved alloy is a chromium steel having a small amount of titanium and being as nearly free from manganese, silicon and aluminum as reasonably possible. More specifically it is a stainless steel of the chromium-titanium type containing from to chromium, about .25% titanium, from .03 to .10% carbon and the balance substantially iron. While the product is superior if manganese, silicon and aluminum be absent, small amounts thereof can be tolerated in the alloy but the manganese and silicon should not exceed .5% and the aluminum should be materially lower, i. e., not over .3%. For example, a steel containing chromium, titanium and industrial applications of Application January 27, 1950, Serial No. 140,955

carbon as stated above and not more than .4% manganese, .3% silicon, .2% aluminum and only residual phosphorus and sulphur, is characterized by a thermal coefficient of 11.l 10 and a residual strain in glass sealed thereto of not'over 200 millimicrons per cm.

In a preferred embodiment of our invention, we provide a heat of steel containing from 15 to 30% chromium, from .1 to 2% titanium, from .03 to .10% carbon, from .01 to 3% silicon, from .1 to 4% manganese, and from .005 to .2% aluminum, by known metallurgical practice. The heat is cast and worked into sheets by conventional methods. The resulting product is found to have spinning characteristics entirely satisfactory for the formation of cones such as used in television tubes, from flat sheet. When a seal to glass is made using this steel, the residual strain produced in the glass is not excessive, i. e., below 200 millimicrons per cm. If the percentage of silicon, manganese or aluminum be substantially greater than the upper limits of the ranges given, the product will have a coefiicient of thermal expansion too high for making a satisfactory seal with glass, in that even if a seal can be made successfully, the residual strain will materially exceed 200 millimicrons per cm. which is about the maximum for practical purposes.

We have also discovered that the thermal coefficient of our steel may be reduced even further, i. e., from 11.l l0 to about 11.2 10- by the addition thereto of from .004 to 1.5% of one or more of the following elements: boron, columbium, molybdenum, nickel, tungsten and vanadium. This reduction of the thermal coefficient permits the residual strain in a glass seal to be further reduced. The individual effect of these elements in reducing residual strain is illustrated in the following table, in which are given the strains produced in a bead of glass deposited on the metallic base constituted by an identical iron-chromium-titanium-carbon alloy containing .06% carbon, 17% chromium, and .40% titanium, plus the indicated percentages of the above elements, the balance being substantially all iron:

We have further discovered that the adverse effect of aluminum in excess of 2% can be counteracted by increasing the titanium content above .4%. Some aluminum is always present in titanium-bearing steel as a result of the use of commercial ferro-titanium oi the low-carbon grade, as-a source of the desired. titanium addition. This group of alloys is made by aluminothermic reduction of titanium ores and commonly carries 6 to 9 per cent metallic aluminum. Since it is a common practice to deoxidize the steel before titanium addition with aluminum, most of the aluminum added as a component. of the titanium alloy is retained in the steel and. may raise the aluminum content to an undesirably high percentage.

The steel of our invention, in addition to-hav.--

ing the desired low coeflicient of thermal expansion, good spinning qualities and resistance to oxidation, is ferritic at all temperatures in the range .to \which. it is-subject in making. a sealwith glassorin subsequent use; This eliminatesdifliculty. which. might. otherwise result from allotropic transformation within such. range.

Weclaim:

1. A ferrous alloy containing from 15 to. 30% chromium, less than 11% manganese. less than 3% silicon, from..005% to 2% aluminum, from .03 to .10% carbon, about 25% titanium, and the balance substantially. all iron, said alloyex.- hibiting good spinning qualities and the ability toforma seal with glass without producing-ex.- cessive residual strain in the latter.

2. A. ferrous alloy containing from 15 to 30 per centchromium, from0103to 0.10pm cent carbon, from: .10:to. 2:00 per cent titanium, from .10 to .40 per cent manganese, from .01 to.30 percent FREEMAN J. PHILLIPS. RAYMOND SMITH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date.

2,024,561 Becket'atal Dec; 17, 1935 2,277,440 Knochel Mar. 24,1942 2,513,241 Holst et a1 June 2'7, 1950 OTHER REFERENCES- Transactions, American. Institute. of. Mining and Metallurgical Engineers,,vo1. 113;,pages 129., 138, 139 and 141.. Published by. the A. I MLEI, New. York.

Alloys. of. Iron and Chromium,, vol; II, High Chromium page 89.. Edited by Kinzel' and Franks. Published. by the. McGraw-Hill'. Book Company,v New York.

Open Hearth Proceedings, vo1. 28, 1945; pages 212 and 214. Publishedin 1945by the A. I. .MLEL, New York. 

1. A FERROUS ALLOY CONTAINING FROM 14 TO 30% CHROMIUM, LESS THAN .4% MANGANESE, LESS THAN .3% SILICON, FROM .005% TO .2% ALUMINUM, FROM .03 TO .10% CARBON, ABOUT .25% TITANIUM, AND THE BALANCE SUBSTANTIALLY ALL IRON, SAID ALLOY EXHIBITING GOOD SPINNING QUANTITIES AND THE ABILITY TO FORM A SEAL WITH GLASS WITHOUT PRODUCING EXCESSIVE RESIDUAL STRAIN IN THE LATTER. 